Once WP8 was released, WP7 got a final, delayed update to WP7.8, which might not be ideal, but is probably better than the Apple equivalent, which would've been to do the same thing but call it WP8 with some features missing.
Now, after 3 years of WP we have the old WP7.8 and the new WP8. That's it - that's all the fragmentation. And pretty much every app written for WP7 will work on 8, and you can still write 7 apps if you don't need the specific features for 8 and they'll work on both. Compare that to the Android situation, and I think you'll find a lot of Android phones are still on 2.x. And that linked graph is for AppBrain users, who are probably more likely than average to have an upgraded device.
Not that it matters, and I'm not particularly an MS fan, but your second paragraph doesn't make a lot of sense (compare iPhone's interoperability with OSX's; and I'm pretty sure MS aren't trying to turn everyone's computer into an Xbox). MS haven't uprooted very much, actually; Bing, S&T and Windows are pretty much the same, except Windows now has a touch-friendly app thing that you can turn off in the free upcoming update. Not really what you're describing.